A quick look at the catseye

[timh]

Just one gap in the clouds recently which I used to try and get my VX12 re-setup, aligned and collimated after needing to swap in a new secondary mirror. To then test things out there was about 1.5 h of clearish sky which I used to image the catseye nebula.

VX12 Orion Optics (UK) Newtonian (f = 1200mm, F4.0), SW parracor type coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, no guiding. ZWO IR/UV cut filter.

AS1294 MM camera - 2072 x 1440 pixels - unlocked 2.315 uM pixels (12 bit ADU) --> 0.4 arcsec/ pixel image scale

586 x 1s exposures at gain 200 brightness 16 and at - 5C. Bortle 6 skies - no moon - ~ midnight on 24/07 so just into true darkness at lat 51.4 N. 600 x 1s masterdark to match created in Sharpcap

Exposures collected in Sharpcap livestacking mode with FWHM filter set to 4.84 (i.e. FWHM in pixels meaning that the filter excluded frames with FWHM > ~ 1.9 arcsec). This filter setting excluded about 70% of the frames. Focus adjusted periodically 'on the fly' to allow for temperature drop as monitored by the livestacking FWHM readings.

An initial set of ~ 1300 x 1s frames was then further culled to a set of 586 x 1s 'best frames' using Subframe selector in Pixinsight to exclude frames with FWHM > 1.7 and those that were insufficiently bright (star number) and/or distorted (Ellipticity). These were calibrated, registered and integrated in Pixinsight - the measured FWHM of the linear 586 x 1s integration image was 1.52 arc sec.

Further processing in PixInsight was as follows. ..

First a 'dynamic PSF' was calculated from the average of 20 stars within the image- this showed an r value of 0.84 - all at a similar angle- indicating that the stars were somewhat elliptical in shape and that (as I later confirmed) I had not got collimation quite right.

Richardson Lucy Deconvolution was applied with the application of both a transparency mask and a blocking star mask (meaning deconvolution would only be applied to the catseye nebula). 120 iterations were used with the settings as below.

Following some masked noise reduction (MLT) the image was stretched using Histogram Transformation and then the contrast within the bright catseye enhanced with 2 successive applications of the LHE (local histogram equalization) process set at default settings except that contrast enhancement was limited to 1.5 and the process was run at 12 bit. A masked MLT noise reduction was then repeated on the now stretched image. Finally curve and contrast/ brightness adjustments were carried out in Affinity and Photoscape.

Overall - despite the collimation being somewhat off and only 10 min of effective imaging time - deconvolution seems to have largely 'mended' distortions. it is starting to show more of the overall complex shape with some of the old 'shells' faintly visible. It is a bit messy around the central star - possibly deconvolution artefact? - It will be interesting to try further with more data, colour data and on a stiller night with better collimation - but promising for what was really only a quick look see.


Tim

[Menno555]

Nice and useful read again Tim!
I still want to use my ASI482MC on planetary nebulae (the clouds here know it though ) and see what the bigger pixel size really can do with my 2000mm focal length.
Your "manuals" can come in handy

Menno